[llvm] Turn off uninitialized warnings for GCC up to 14. (PR #147968)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `clang-aarch64-sve-vla-2stage` running on `linaro-g3-02` while building `llvm` at step 12 "ninja check 2".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/41/builds/7843

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 12 (ninja check 2) failure: stage 2 checked (failure)
******************** TEST 'LLVM :: tools/llvm-exegesis/RISCV/rvv/filter.test' FAILED ********************
Exit Code: 2

Command Output (stderr):
--
/home/tcwg-buildbot/worker/clang-aarch64-sve-vla-2stage/stage2/bin/llvm-exegesis -mtriple=riscv64 -mcpu=sifive-x280 -benchmark-phase=assemble-measured-code --mode=inverse_throughput --opcode-name=PseudoVNCLIPU_WX_M1_MASK     --riscv-filter-config='vtype = {VXRM: rod, AVL: VLMAX, SEW: e(8|16), Policy: ta/mu}' --max-configs-per-opcode=1000 --min-instructions=10 | /home/tcwg-buildbot/worker/clang-aarch64-sve-vla-2stage/stage2/bin/FileCheck /home/tcwg-buildbot/worker/clang-aarch64-sve-vla-2stage/llvm/llvm/test/tools/llvm-exegesis/RISCV/rvv/filter.test # RUN: at line 1
+ /home/tcwg-buildbot/worker/clang-aarch64-sve-vla-2stage/stage2/bin/llvm-exegesis -mtriple=riscv64 -mcpu=sifive-x280 -benchmark-phase=assemble-measured-code --mode=inverse_throughput --opcode-name=PseudoVNCLIPU_WX_M1_MASK '--riscv-filter-config=vtype = {VXRM: rod, AVL: VLMAX, SEW: e(8|16), Policy: ta/mu}' --max-configs-per-opcode=1000 --min-instructions=10
+ /home/tcwg-buildbot/worker/clang-aarch64-sve-vla-2stage/stage2/bin/FileCheck /home/tcwg-buildbot/worker/clang-aarch64-sve-vla-2stage/llvm/llvm/test/tools/llvm-exegesis/RISCV/rvv/filter.test
PseudoVNCLIPU_WX_M1_MASK: Failed to produce any snippet via: instruction has tied variables, avoiding Read-After-Write issue, picking random def and use registers not aliasing each other, for uses, one unique register for each position
FileCheck error: '<stdin>' is empty.
FileCheck command line:  /home/tcwg-buildbot/worker/clang-aarch64-sve-vla-2stage/stage2/bin/FileCheck /home/tcwg-buildbot/worker/clang-aarch64-sve-vla-2stage/llvm/llvm/test/tools/llvm-exegesis/RISCV/rvv/filter.test

--

********************


```

</details>

https://github.com/llvm/llvm-project/pull/147968